Circuit board, mounting structure of ball grid array, electro-optic device and electronic device

ABSTRACT

In a circuit board including a pad for mounting a ball grid array and a wiring, a mounting structure of the ball grid array, an electro-optic device, and an electronic device, the circuit board includes a pad for mounting the ball grid array, a wiring for connecting the pad and an external terminal, and a soldering resist having an opening portion exposing the pad and the wiring.

BACKGROUND OF THE INVENTION

[0001] 1. Technical Field

[0002] The present invention relates to a circuit board, a mountingstructure of a ball grid array, an electro-optic device, and anelectronic device. More particularly, the present invention relates to acircuit board, a mounting structure of a ball grid array, anelectro-optic device, and an electronic device, in which the printingmargin of a soldering material is increased upon mounting the ball gridarray on the circuit board by reflow processing.

[0003] 2. Related Art

[0004] According to a widespread conventional method, a QFP (Quad FlatPackage) is mounted on a printed circuit board (PCB) as a mountingmethod corresponding to the fine pitch or the multi-pin structure of alead terminal of a semiconductor device. According to the method, theQFP as a flat package having a large number of gull-wing lead terminalsat four sides of the package is generally mounted on the PCB containingresin. Further, the QFP is used while it is electrically connected to aconductive portion of the PCB.

[0005] However, in accordance with the further fine pitch or multi-pinstructure, the QFP has a problem that the reliability of the connectionis deteriorated due to a short circuit caused by a soldering bridge uponmounting or the shortage of soldering. In addition, the QFP has anotherproblem that the mounting area on the PCB is increased corresponding toan externally projected portion of the lead terminal from the package.

[0006] Then, in order to respond to the further fine pitch or multi-pinstructure of the semiconductor device, a mounting method using a ballgrid array (hereinafter, referred to a BGA) or a chip size package(hereinafter, referred to as CSP) and a printed circuit board formounting it are proposed.

[0007] Referring to FIG. 25, a single printed-circuit board hassemiconductor package lands 382 and 384 having different shapes and, onthe printed-circuit board, lands to which terminals having the samefunction are connected by a pattern wiring 388. If changing the shape ofthe package mounted on the printed circuit board, the sameprinted-circuit board is used without manufacturing anotherprinted-circuit board.

[0008] Further, according to another mounting method, an electric partin which the exchange and the maintenance of the BGA, etc. are notpossible is soldered so as to prevent the soldering defect. Asschematically shown in a flowchart of FIG. 26, specifically, a mountingmethod 290 includes: a step 291 of printing cream soldering on apredetermined position on the PCB; a step 292 of mounting, by a mounter,a semiconductor device with a bump such as the BGA (including a chipsize package (CSP) with a pitch of not more than 0.8 mm) at apredetermined position on the PCB to which the cream soldering isprinted; a step 293 of performing an X-ray inspection and of selectingwhether or not the semiconductor device is defective; and a step 294 ofheating only the nondefective semiconductor device passing the X-rayinspection by reflow processing and mounting.

[0009] Further, referring to FIGS. 27(a) to (d), according to anothermounting method of the BGA, a cream soldering 312 is coated to a cave(recessed) portion 311 arranged on a board 310.

[0010] Specifically, referring to FIG. 27(a), the board 310 having aplurality of cave portions 311 on its surface is provided. Referring toFIG. 27(b), the cream soldering 312 is coated to the plurality of caveportions 311. Furthermore, referring to FIG. 27(c), a bump 317 of a BGA315 is positioned to the plurality of cave portions 311. In addition,referring to FIG. 27(d), the bump 317 is mounted by reflow processingand is pressed and bonded.

[0011] According to another method, referring to FIGS. 28(a) to (c), asemiconductor device 345 with a bump is thermally bonded to a pad 341 ofa board 343 via an Anisotropic Conductive Film (hereinafter, referred toas an ACF) 349.

[0012] According to the mounting method using the ACF 349, in the CSP inwhich the pitch of the bump 347 is narrow, for example, it is 0.1 mm to0.5 mm, the short circuit between the adjacent bumps is efficientlyprevented. Advantageously, a large number of bumps 347 are electricallyconnected.

[0013] However, on the convention printed-circuit board, upon mountingthe semiconductor device with a fine bump, e.g., the BGA, a solderingmaterial as a conductive material must be precisely printed onto a fineland (pad). Thus, the conventional printed-circuit board has a problemthat the position for printing and the printing operation take a longtime and the position of the printed soldering material is easilydeviated from the pad. In particular, since the CSP has a further finepitch as compared with the BGA, it is difficult to print the solderingmaterial precisely and mount it on the land (pad) of the printed circuitboard on which the FPC is easily modified.

[0014] According to the mounting method as shown in FIG. 26, the X-rayinspection must be performed before the heating using reflow processing.Therefore, the mounting method has a problem that the number of steps isincreased, the manufacturing management is complicated, and themanufacturing time is long. Since the cream soldering must precisely beprinted on the fine pad, the positioning for printing and the printingoperation take a long time.

[0015] According to the mounting method as shown in FIG. 27, it isdifficult to form the pad having the cave portion. Further, since thesoldering must be precisely printed to the pad having the fine caveportion, the mounting method has a problem that the positioning forprinting and the printing operation take a long time.

[0016] Further, the mounting method using the ACF has problems that notonly the costs of the ACF are increased but also mounting simultaneouslyto another device is not performed. That is, the ACF which is thermallybonded and mounted, and the other device mounted by the soldering reflowprocessing must be mounted independently in consideration of thedifferent mounting processes.

[0017] As a result of considering the above problems, it has beendiscovered that by providing a soldering resist having an openingportion which is open so that the entire or a part of the pad and wiringconnected to the BGA is exposed, the coating margin (printing margin) ofthe soldering material is increased, the printing deviation due to thesetting of an uneven portion of the resist is not caused, and thus thesoldering material is coated precisely and easily. Further, the defectfor connection is caused due to the deviation of printing of thesoldering material. In this case, it is found that the solderingmaterial out of the pad due to the printing deviation returns to the padupon reflowing by its fluid property, irrespective of the deviation oruneven portion of the resist.

[0018] As such, it is an object of the present invention to provide acircuit board in which the mounting position of a BGA (including theCSP) is not deviated due to the coating defect of the soldering materialwhen the BGA is mounted by reflow processing via the soldering material,a mounting structure of the BGA using the circuit board, anelectro-optic device, and an electronic device.

SUMMARY

[0019] In order to solve the above-mentioned problems, according to thepresent invention, there is provided a circuit board comprising: a padfor mounting a BGA; a wiring for connecting the pad and an externalterminal; and a soldering resist, wherein the soldering resist has anopening portion exposing the pad and the wiring.

[0020] The above-mentioned structure facilitates the coating of thesoldering material and increases the coating margin of the solderingmaterial.

[0021] Preferably, when the area of the mounted BGA is 100%, the area ofthe opening portion has a value within a range of 50% to 150%.

[0022] The above-mentioned structure facilitates the coating of thesoldering material and increases the coating margin of the solderingmaterial.

[0023] Further, preferably, the soldering resist or its end portionexists at the position of 0.1 mm toward the inner region from the outercircumference in the portion for mounting the BGA in the structure ofthe circuit board according to the present invention.

[0024] With the above structure, since an end portion of the BGA has thesoldering resist, a short-circuited edge is effectively prevented.

[0025] In the circuit board according to the present invention,preferably, when the pitch of the bump of the mounted BGA has a narrowportion less than 0.6 mm and a wide portion not less than 0.6 mm, theopening portion of the soldering resist is arranged in accordance withthe pad corresponding to the narrow portion of the BGA.

[0026] With the above-mentioned structure, the design of the circuitboard is easily performed, irrespective of the pitch of the bump.

[0027] Preferably, in the circuit board according to the presentinvention, the thickness of the soldering resist is 1% to 50% of theheight of the bump of the mounted BGA.

[0028] With the above-mentioned structure, the advantages for thesoldering resist and the advantage for preventing the short-circuitededge are obtained. The soldering resist is easily formed.

[0029] In the circuit board according to the present invention, a padfor mounting an electronic element other than the BGA is provided.Preferably, the soldering resist exists near the pad.

[0030] With the above-mentioned structure, the electronic element otherthan the BGA can easily be mounted together with the BGA.

[0031] Further, in order to solve the above-mentioned problems,according to another embodiment of the present invention, there isprovided a mounting structure of a BGA for mounting the BGA on a circuitboard, wherein the circuit board includes: a pad for mounting the BGA; awiring; and a soldering resist. The soldering resist has an openingportion for exposing the pad and the wiring.

[0032] That is, with the above-mentioned structure, the margin is widewhen the soldering material is coated. Even upon mounting the BGA or theCSP on the circuit board, the deviation of the mounting position issuppressed.

[0033] With the mounting structure of the BGA according to the presentinvention, preferably, an under-fill is filled between the BGA and thecircuit board with the following properties:

[0034] (1) volume resistance having a value within a range of 1×10⁶ to1×10²⁰ Ω·cm,

[0035] (2) tensile strength having a value within a range of 1 to 200MPa, and

[0036] (3) Break stretch having a value within a range of 10% to 500%.

[0037] The above-mentioned structure provides the mounting structure ofthe BGA in which environmental stability and mechanical strength areimproved.

[0038] In order to solve the above-mentioned problems, according toanother embodiment of the present invention, there is provided anelectro-optic device comprising a BGA, as a driving element or a powersupply element, mounted on a circuit board comprising: a pad formounting the BGA; a wiring for connecting the pad and an externalterminal; and a soldering resist having an opening portion for exposingthe pad and the wiring.

[0039] That is, the above-mentioned structure effectively provides theelectro-optic device using the circuit board in which the deviation ofmounting position of the BGA is suppressed.

[0040] In order to solve the above-mentioned problems, according toanother embodiment of the present invention, there is provided anelectronic device comprising the electro-optic device and control meansfor controlling the electro-optic device.

[0041] That is, the above-mentioned structure effectively provides theelectronic device including the electro-optic device using the circuitboard in which the deviation of mounting position of the BGA issuppressed.

BRIEF DESCRIPTION OF THE DRAWINGS

[0042]FIG. 1 is a diagram for explaining a circuit board according to afirst embodiment.

[0043]FIG. 2 is one cross-sectional view for explaining the position ofa soldering resist on the circuit board (No. 1).

[0044]FIG. 3 is another cross-sectional view for explaining the positionof the soldering resist on the circuit board (No. 2).

[0045]FIG. 4 is a diagram for explaining a method for simultaneouslymounting a BGA and another electronic element on the circuit board.

[0046]FIG. 5 is a diagram for explaining an FPC.

[0047]FIG. 6 is one diagram for explaining the distance between adjacentpads (No. 1).

[0048]FIG. 7 is another diagram for explaining the distance between theadjacent pads (No. 2).

[0049]FIG. 8 is a diagram showing the shape of pad.

[0050] FIGS. 9(a) to (d) are a diagram showing the shapes of modifiedpads.

[0051] FIGS. 10(a) to (c) are one diagram showing the plan shapes of themodified pads.

[0052] FIGS. 11(a) and (b) are another diagram showing the plan shapesof the modified pads.

[0053]FIG. 12 is a cross-sectional view for explaining one structure ofthe BGA (No. 1).

[0054]FIG. 13 is a cross-sectional view for explaining another structureof the BGA (No. 2).

[0055]FIG. 14 is a cross-sectional view for explaining another structureof the BGA (No. 3).

[0056]FIG. 15 is a cross-sectional view for explaining the structure ofa WCSP.

[0057] FIGS. 16(a) and (b) are a diagram for explaining a bump in amounting structure of a semiconductor device with the bump according toa modification of the first embodiment.

[0058]FIG. 17 is a diagram for explaining a mounting structure of asemiconductor device with a bump according to a second embodiment.

[0059]FIG. 18 is a diagram for explaining an under-fill.

[0060] FIGS. 19(a) and (b) are a diagram showing processes forexplaining one method for mounting the BGA on a circuit board (No. 1).

[0061] FIGS. 20(a) and (b) are a diagram showing processes forexplaining another method for mounting the BGA on the circuit board (No.2).

[0062] FIGS. 21(a) and (b) are a diagram showing processes forexplaining another method for mounting the semiconductor device with thebump on the circuit board (No. 3).

[0063]FIG. 22 is a perspective view schematically showing the appearanceof a liquid crystal panel according to a third embodiment of the presentinvention.

[0064]FIG. 23 is a cross-sectional view schematically showing thestructure of a panel according to the third embodiment.

[0065]FIG. 24 is a block diagram schematically showing the structure ofan electronic device according to a fourth embodiment.

[0066]FIG. 25 is a diagram for explaining a conventional circuit board.

[0067]FIG. 26 is a flowchart for explaining a conventional mountingmethod of a BGA.

[0068]FIG. 27 is a diagram for explaining a mounting method of the BGAusing a cave portion arranged on a conventional PCB.

[0069]FIG. 28 is a diagram for explaining a mounting method of asemiconductor device with a bump using an Anisotropic Conductive Film(ACF).

DETAILED DESCRIPTION

[0070] Hereinbelow, a description is given of a circuit board, amounting structure of a BGA, an electro-optic device using it, and anelectronic device according to embodiments of the present invention withreference to the drawings.

[0071] The embodiments of the present invention indicate examples and donot limit the present invention and, they can arbitrarily be changedwithin a range of the present invention.

First Embodiment

[0072] According to a first embodiment, referring to FIG. 1, a circuitboard comprises: a pad 413 a for mounting a BGA; a wiring 411 forconnecting the pad 413 a and an external terminal; a soldering resist431. In the circuit board, the soldering resist 431 has an openingportion 433 for exposing the pad 413 a and the wiring 411.

[0073] 1. Circuit Board

[0074] (1) Soldering Resist

[0075] 1) Area of Opening Portion

[0076] If the area of the mounted BGA is 100%, preferably, the area ofthe opening portion in the soldering resist has a value within a rangeof 50% to 150%.

[0077] Because when the area of opening portion in the soldering resisthas a value of 50% or less, the design for the pad or the wiring isexcessively limited. Further, when the area of the opening portion inthe soldering resist is over 150%, the occurrence of a short-circuitededge may not be effectively prevented. When the area of the openingportion is over 100%, the short-circuited edge may be caused; however,this is effectively prevented by adjusting the height of the bump or byfilling with an under-fill.

[0078] Therefore, when the area of the mounted BGA is 100%, the area ofthe opening portion in the soldering resist is more preferably within arange of 60% to 99%. Even more preferably, it is within a range of 70%to 90%.

[0079] 2) Position 1

[0080] Referring to FIG. 2, preferably, the soldering resist 431 or itsend portion exists at the position of at least 0.1 mm toward the innerregion from the outer circumference in the portion for mounting the BGA11.

[0081] Because, when the soldering resist or its end portion does notexist at the position of at least 0.1 mm toward the inner region fromthe outer circumference in the portion for mounting the BGA, it isdifficult to effectively prevent the occurrence of the short-circuitededge upon mounting the BGA.

[0082] However, when an excessive amount of soldering resist existstoward the inner region from the outer circumference, the design of thepad or the wiring may be largely limited.

[0083] Therefore, more preferably, the soldering resist or its endportion exists within a range of 0.11 mm to 1 mm toward the inner regionfrom the outer circumference in the position for mounting the BGA. Evenmore preferably, the soldering resist or its end portion exists within arange of 0.15 mm to 0.5 mm toward inner region from the outercircumference.

[0084] 3) Position 2

[0085] Preferably, referring to FIG. 3, when the pitch of a bump 13 ofthe mounted BGA 11 includes both a narrow portion less than 0.6 mm and awide portion not less than 0.6 mm, only a pad 17 corresponding to thenarrow pitch of the bump 13 of the BGA 11 has an opening portion 433 inthe soldering resist 431.

[0086] Because the arrangement of the opening portion at the narrow padcorresponding to the BGA responds to the varied pitch of the bump withthe above structure, the circuit board is easily designed. That is, atthe pad corresponding to the wide pitch of the BGA, the coating marginof the soldering material can be wide without providing an openingportion.

[0087] 4) Thickness

[0088] Referring to FIG. 2, preferably, the thickness of the solderingresist 431 is within a range of 1% to 50% of the height of the bump 13of the mounted BGA 11.

[0089] Because the thickness of soldering resist is limited, theadvantage of the soldering resist and the advantage for preventing theshort-circuited edge is obtained. Further, the soldering resist iseasily formed.

[0090] More preferably, the thickness of the soldering resist is 1% to40% of the height of the bump of the mounted BGA. Even more preferably,it is 1% to 30% thereof.

[0091] 5) Another Opening Portion

[0092] Referring to FIG. 4, preferably, a pad 38 for mounting anelectronic element 39 other than the BGA is provided and the solderingresist 431 adjacently exists around the pad 38.

[0093] With the above-mentioned structure, the electronic element otherthan the BGA is easily and simultaneously mounted on the circuit boardtogether with the BGA.

[0094] (2) Circuit Board

[0095] 1) Type

[0096] The type of circuit board includes ones made of rigid glass epoxyPCB and ceramic PCB and, however, it is not limited to those.Preferably, referring FIG. 5, the FPC is formed by mounting a metallicwiring on materials made of polyimide resin or polyester resin, and itis used for a cellular phone, etc. because it is light and thin and canbe bent.

[0097] That is, referring to FIG. 5, a flexible substrate 141 comprisesa plurality of pads 147. Further, by using an FPC 140 having sprocketsat both ends thereof, a semiconductor device with the bump iscontinuously mounted.

[0098] 2) Pitch 1 of pad

[0099] Referring to FIG. 6, when the pitch of a pad 413 a is defined bythe distance from the center position between the pads to the centerposition between the adjacent pads, namely, CTC (Center to Center),preferably, the pitch of the pad is within a range of 0.4 mm to 1.0 mm.

[0100] Because, when the pitch of the pad is less than 0.4 mm, thewiring cannot be pulled out and the width of wiring needs to beexcessively narrow. Further, the soldering bridge is frequently caused.

[0101] When the pitch of the pad is more than 1 mm, the number of padsis excessively limited and it might be difficult to mount the CSP or BGAhaving the multi-pin structure.

[0102] Therefore, more preferably, the pitch of the pad is within arange of 0.45 mm to 0.8 mm. Even more preferably, it is within a rangeof 0.5 mm to 0.6 mm.

[0103] 3) Pitch 2 of pad

[0104] Preferably, referring to FIG. 7(a), near the center of a bottom433 of the BGA, a region 433 a is arranged with the pitch of the pad inthe longitudinal direction and the pitch of the pad in the lateraldirection different therefrom.

[0105] Because, when the wiring is concentratedly pulled out near thecenter of the bottom of the BGA, the arrangement of the region havingthe different pitches enables the wiring in any of the longitudinaldirection and the lateral direction in which the wide pitch is providedto preferentially be pulled out.

[0106] Preferably, referring to FIG. 7(b), a region 433 b is provided ina peripheral area of the bottom 433 of the BGA with the pitch of the padin the longitudinal direction and that of the pitch of the pad in thelateral direction different therefrom.

[0107] Because when the wiring to the outside is concentratedly pulledout near the peripheral area of the bottom of the BGA, the arrangementof the region having the different pitches enables the wiring in any ofthe longitudinal direction and the lateral direction in which the widepitch is provided to preferentially be pulled out.

[0108] 4) Area of Pad

[0109] Preferably, the area of the pad has a value within a range of0.01 mm² to 0.5 mm².

[0110] Because, when the area of the pad has a value less than 0.01 mm²,it is difficult to coat the soldering material and the electricconnection to the BGA may be unstable.

[0111] Further, when the area of the pad has a value more than 0.5 mm²,it is difficult to pull out the wiring, the width of wiring may becometoo narrow, and s soldering bridge may frequently occur.

[0112] Hence, more preferably, the area of the pad has a value within arange of 0.03 mm² to 0.3 mm². Even more preferably, it has a valuewithin a range of 0.05 mm² to 0.1 mm².

[0113] 5) Plan Shape of Pad

[0114] Referring to FIG. 8, preferably, the plan shape of the pad iscircular or square. Because the plan shape causes the formation of thepad with high reproducibility and further causes the efficient use ofthe entire pad.

[0115] Preferably, the plan shape of the pad is non-circular ornon-square. For example, referring to FIG. 9(a), it is elliptic.Referring to FIG. 9(b), it is diamond-shaped. Referring to FIG. 9(c), itis modified-rectangular (H-shape). Referring to FIG. 9(d), it isrectangular-round shaped. Referring to FIG. 10(a), it is semi-elliptic(half-elliptic). Referring to FIG. 10(b), it is semi-diamond-shaped(half-diamond or triangular). Referring to FIG. 10(c), it issemi-rectangular-round shaped (half rectangular-round). Referring toFIG. 11(a), it is semi-circular, (half circular). Referring to FIG.11(b), it is semi-polygonal (half polygonal). Alternatively, preferably,it is at least one of ⅓-circular, ⅔-circular, ⅕-circular, ⅖-circular,⅗-circular, and ⅘-circular shapes.

[0116] Because the modified pad has the plan shape, thus, the rate forpreventing the pull-out of the wiring is reduced, the margin forpositional deviation is widely ensured upon coating the solderingmaterial, and the manufacturing efficiency of the circuit board isimproved. Further, the pad having the above plan shape is formed withhigh reproducibility.

[0117] 2. BGA

[0118] (1) Type

[0119] The type of the BGA applied to the present invention is notlimited. Preferably, the type of the BGA is, e.g., BGAs 60, 70, and 80as shown in FIGS. 12 to 14 so as to easily respond to the fine pitch andthe multi-pin structure of the wiring. Alternatively, it is a waferlevel chip size package (WCSP) 90 as shown in FIG. 15.

[0120] Referring to FIG. 12, a BGA 60 is a semiconductor device with abump comprising: a bear chip 61; an interposer 63 for mounting the bearchip 61 by a wiring bonding 68; and bumps (soldering balls) 65 which arearranged like an area array with the pitch of 0.6 mm to 2.54 mm on theback surface of the interposer 63.

[0121]FIG. 13 shows a BGA 70 which is obtained by a so-called flip chipmethod by which bumps 71 are previously formed on a bonding pad 75 ofthe bear chip 61, and are connected to inner leads (not shown) on theinterposer 63 by thermal soldering reflow processing or ultrasonicvibration in a state in which pressure is applied.

[0122]FIG. 14 shows a BGA 80 which is obtained by a so-called TAB (TapeAutomated Bonding) method by which bumps are previously formed to innerleads on a tape or the bear chip 61 and they are connected by theinner-lead bonding.

[0123] Referring to FIG. 15, a WCSP is a CSP comprising, at the waferstage, a wiring 103, electric insulating films 97 and 107, and bumps(soldering balls) 93 which are arranged like an area array with thepitch of 0.1 mm to 1.0 mm, not via an interposer. In particular, upondesiring a thin, light, and compact mounting structure, the WCSP is asemiconductor device with the best bump.

[0124] (2) Bump

[0125] The form of the bump provided for the BGA is not limited;however, referring to FIG. 16(a), preferably, the edge portion of a bump113 is flat.

[0126] Because, when the BGA is positioned and mounted onto the pad ofthe circuit board, the bump uniformly flows around the pad and the bumpof the BGA and the pad are strongly fixed.

[0127] Preferably, referring to FIG. 16(b), as the bump arranged to theBGA, a cave (recessed) portion is provided onto the surface of the edgeportion of the bump 113.

[0128] Because the above structure causes the existence of the solderingmaterial via the cave portion between the bump of the BGA and the pad,these members are strongly fixed.

[0129] (3) Soldering Material

[0130] 1) Type

[0131] The type of the soldering material adhered to the bump is notlimited. For example, it is a commonly-used soldering materialcontaining Sn or Pb/Sn, or flux material such as resin or common rosin.Preferably, the type of the soldering material is one obtained bycombining a soldering containing Cu/Sn/Ag without Pb and the fluxmaterial.

Second Embodiment

[0132] According to a second embodiment, referring to FIG. 17, a circuitboard 361 comprises a pad 363 for mounting a BGA (interposer) 63, awiring (not shown), and a soldering resist 367. Further, the solderingresist 367 has an opening portion 369 which is opened so that the entireor part of the pad 363 and wiring connected to the BGA 63 is exposed. Ina mounting structure 360 of the BGA, the BGA 63 is mounted on thecircuit board 361.

[0133] Hereinbelow, the same portions as those according to the firstembodiment are omitted and features according to the second embodimentare mainly described.

[0134] 1. Structure

[0135] (1) Basic Structure

[0136] The mounting structure 360 of the BGA according to the secondembodiment basically comprises: the BGA 63; the circuit board 361; and asoldering material 365. The BGA 63, the circuit board 361, and thesoldering material 365 are the same as those according to the firstembodiment and they are not described here.

[0137] (2) Under-Fill

[0138] According to the second embodiment, referring to FIG. 18,preferably, an under-fill 64 having the following properties is filledbetween a semiconductor device with a bump (BGA) and the circuit board361.

[0139] 1) volume resistance having a value within a range of 1×10⁶ to1×10²⁰ Ω·cm.

[0140] 2) tensile strength having a value within a range of 1 to 200MPa.

[0141] 3) break stretch having a value within a range of 10% to 500%.

[0142] Hereinbelow, a detailed description is given of preferred typesof the under-fill and the preferred property thereof.

[0143] 1) Type

[0144] Preferably, the type of the under-fill is one containingthermosetting resin and photo-curing resin and, alternatively, it is oneof them.

[0145] Because the use of the curing resin satisfies the basicproperties as the under-fill including mechanical strength and moistureresistance.

[0146] Preferably, epoxy resin or silicon resin is used as thethermosetting resin; as the photo-curing resin, epoxy resin, acrylicresin, and silicon resin are used.

[0147] Preferably, when it is desired that the under-fill have a shadingor shielding property, a shading material, e.g., carbon particles,carbon fiber, or pigment is added to the curing resin. Alternatively, anultraviolet absorbing agent or fluorescent brightening agent is added.

[0148] As a result of adding these compounds, light entering from theoutside is effectively absorbed or the wavelength thereof is convertedinto light having a wavelength which prevents optically erroneousoperation.

[0149] 2) Volume Resistance

[0150] Preferably, the volume resistance of the under-fill is within arange of 1×10⁶ to 1×10² Ω·cm.

[0151] Because, when the volume resistance of the under-fill is lessthan 1×10⁶ Ω·cm, the insulation between the adjacent bumps becomesinsufficient. When the volume resistance of the under-fill is over1×10²⁰ Ω·cm, the selection of available materials is remarkably limited.

[0152] Therefore, more preferably, the volume resistance of theunder-fill is within a range of 1×10⁸ to 1×10¹⁸ Ω·cm. Even morepreferably, it is within a range of 1×10¹⁰ to 1×10¹⁶ Ω·cm.

[0153] 3) Tensile Strength

[0154] Preferably, the tensile strength of the under-fill is within arange of 1 to 200 MPa.

[0155] Because, when the tensile strength of the under-fill is less than1 MPa, the mechanical strength is reduced and resistance stability andthermal tolerance are reduced in the mounting structure of thesemiconductor device with the bump. When the tensile strength of theunder-fill is over 200 MPa, the selection of available materials isextremely limited, the strain of stress is excessively caused, and thestability for resistance is deteriorated in the mounting structure ofthe semiconductor device with the bump.

[0156] Thus, more preferably, the tensile strength of the under-fill iswithin a range of 5 to 100 MPa. Even more preferably, it is within arange of 10 to 50 MPa.

[0157] 4) Break Stretch

[0158] Preferably, the break stretch of the under-fill is within a rangeof 10% to 500%.

[0159] Because, when the break stretch of the under-fill is less than10%, the flexibility is deteriorated and the stability for resistanceand the thermal tolerance are deteriorated in the mounting structure ofthe semiconductor device with the bump. When the break stretch of theunder-fill is over 500%, the selection of available materials isextremely limited, and the mechanical strength is reduced.

[0160] More preferably, the break stretch of the under-fill is within arange of 30% to 300%. Even more preferably, it is within a range of 50%to 200%.

[0161] 2. Mounting Method

[0162] (1) First Mounting Method

[0163] Preferably, referring to FIG. 19, the BGA 63 is mounted on thecircuit board 361 having the soldering resist 367 in the following steps(A) and (B) according to the first mounting method.

[0164] (A) A step of coating the soldering material 365 on the pad 363on the circuit board 361 having the soldering resist 367.

[0165] (B) A step of mounting the BGA 63 on the pad 363 which is coatedwith the soldering material 365 by reflow processing.

[0166] With the foregoing, the soldering material is coated by using aconventional coating device, e.g., a silkscreen printing device.Further, the BGA is mounted on the circuit board by using a conventionalreflow device.

[0167] Preferably, after positioning the BGA to the pad on the circuitboard, it is subjected to reflow processing. In this case, preferably,the BGA previously has a positioning mark as a mark and the BGA ispositioned on the pad.

[0168] (2) Second Mounting Method

[0169] Preferably, referring to FIG. 20, a BGA 11 is mounted on acircuit board 19 having a soldering resist 431 in the following steps(A′) and (B) according to the second mounting method.

[0170] (A′) A step of coating a soldering material 15 on a bump 13 ofthe BGA 11.

[0171] (B) A step of mounting the BGA 11, which is coated with thesoldering material 15, on the pad 17 by reflow processing.

[0172] The above operations cause the omission of a positioning stepupon coating the soldering material on the pad, and the BGA is preciselymounted, by reflow processing, on the circuit board such as the FPCwhich is relatively easily modified. That is, the BGA or CSP is mountedon the circuit board, particularly, the FPC by reflow processing at highspeed and with low costs. Further, a mounting method of the BGA isprovided with suppressed defects for mounting.

[0173] (3) Third Mounting Method

[0174] Preferably, referring to FIG. 21, the BGA 11 is mounted on thecircuit board 19 having the soldering resist 431 in the following steps(A″), (A′″), and (B′) according to third mounting method.

[0175] (A″) A step of coating one part 21 of the soldering material onthe pad 17 on the circuit board 19.

[0176] (A′″) A step of coating another part 15 of the soldering materialon the bump 13 of the BGA 11.

[0177] (B′) A step of mounting the BGA 11, which the soldering material15 is partly coated, on the pad 17 to which the soldering material 21 ispartly coated, by reflow processing.

[0178] With the foregoing operation, the BGA is precisely mounted on thecircuit board, in particular, the FPC by reflow processing. Further, themounting method for strongly mounting the BGA is provided.

[0179] (4) Reflow Processing Condition

[0180] Upon using the first to third mounting methods, the reflowprocessing condition is not limited; however, preferably, the heatprocessing is performed by using infrared or heated inert gas underconditions that the peak temperature range is 200° C. to 300° C. and theheating time is 5 sec to 10 min.

[0181] Preferably, during reflow processing, the reflow processing isperformed in an inert state so as to prevent the oxidization of thesoldering material.

[0182] (5) Simultaneous Mounting with Another Element

[0183] Preferably, referring to FIG. 4, according to the first to thirdmounting methods, the BGA 11 and another electronic element 39 such as acapacitor are simultaneously mounted on the circuit board 19 having thesoldering resist 431.

[0184] Because the BGA and the other electronic element including thecapacitor are simultaneously mounted, the number of steps of mountingusing the ACF other than reflow processing is reduced. Therefore, thestep of mounting the BGA is entirely simple and fast.

[0185] Conventionally, the electronic element such as the capacitor or aresistor, other than the BGA, is mounted by reflow processing. However,since the BGA is mounted by ACF, there is a problem that the BGA must bemounted by another mounting method.

Third Embodiment

[0186] According to a third embodiment, an electro-optic devicecomprises a BGA, as a driving element or a power supply element, whichis mounted on a circuit board comprising a pad for mounting the BGA, awiring, and a soldering resist, wherein the circuit board includes anopening portion which is open so that the entire or a part of the padand wiring connected to the BGA is exposed.

[0187] Hereinbelow, a description is given of a liquid crystal panelforming the electro-optic device shown in FIG. 22.

[0188] First, a description is given of the schematic structure of aliquid crystal panel 200 shown in FIG. 22 with reference to FIG. 23.FIG. 23 is a diagram schematically showing a state before mounting asemiconductor device (IC) and a flexible printed-circuit board (FPC) ofthe liquid crystal panel 200 shown in FIG. 22. The dimensions in FIG. 23are appropriately adjusted for the sake of the convenience and selectcomponents in FIG. 23 are properly omitted.

[0189] The liquid crystal panel 200 comprises: a color filter substrate210; an opposed substrate 220 of the color filter substrate 210, whichis adhered thereto by a sealing material 230; and a liquid crystalmaterial 232. The color filter substrate 210 comprises: a firstsubstrate 211 having thereon reflecting layers 212 and a plurality ofcoloring layers 214; a surface protecting layer 215; and a transparentelectrode 216 on the layer structure thereof. As mentioned above, thetransparent electrode 216 is connected to a wiring 218A, the wiring 218Apasses between the sealing member 230 and the first substrate 211, andit is pulled out onto a substrate extended portion 210T. The substrateextended portion 210T has thereon an input terminal portion 219.

[0190] Further, the substrate extended portion 210T comprises: a pad formounting the BGA; a wiring for connecting the pad and an externalterminal; and a soldering resist having an opening portion for exposingthe pad and the wiring. Furthermore, the substrate extended portion 210Tcomprises: a BGA 227 as a driving element or a power supply element ofthe liquid crystal panel 200.

[0191] Consequently, the soldering material is precisely coated to thepad of the substrate extended portion 210T with the wide margin. In thecase of mounting the BGA as a semiconductor device with the fine bumpstructure, the substrate exposed portion 210T is provided with thesuppressed positional deviation of the BGA, which is caused by thecoating defect of the soldering material.

[0192] Thus, the driving of the liquid crystal using the BGA is stableand the liquid crystal panel obtains excellent tolerance.

Fourth Embodiment

[0193] A detailed description is given of the case of using anelectro-optic device as a display device of an electronic deviceaccording to an embodiment.

[0194] (1) Outline of Electronic Device

[0195]FIG. 24 is a diagram showing the entire structure of theelectronic device according to the fourth embodiment. The electronicdevice comprises: a liquid crystal panel 180; and control means 190 forcontrolling the liquid crystal panel 180. Referring to FIG. 24, theliquid crystal panel 180 is conceptually divided into a panel structure180A and a driving circuit 180B comprising a semiconductor IC.

[0196] Preferably, the control means 190 comprises: a displayinformation output source 191; a display information processing circuit192; a power supply circuit 193; and a timing generator 194.

[0197] Preferably, the display information output source 191 comprises:a memory having a ROM (Read Only Memory) or a RAM (Random AccessMemory); a storage unit having a magnetic recording disk and an opticalrecording disk; and a tuning circuit for synchronously outputting adigital image signal. Further, the display information output source 191supplies display information as a predetermined-format image signal tothe display information processing circuit 192 based on various clocksignals generated by the timing generator 194.

[0198] Preferably, the display information processing circuit 192comprises well-known circuits of a serial/parallel converting circuit,an amplifying and inverting circuit, a rotation circuit, a gammacorrecting circuit, and a clamping circuit, and executes processing ofthe input display information, thereby supplying the image informationand a clock signal CLK to the driving circuit 180B. Preferably, thedriving circuit 180B comprises: a scanning line driving circuit; a dataline driving circuit; and an inspecting circuit. The power supplycircuit 193 has a function for supplying predetermined voltages to theabove components.

[0199] (2) Example

[0200] An electro-optic device according to the present inventionincludes, for example, a liquid crystal display device, an organicelectro-luminescence device, an inorganic electro-luminescence device, aplasma display device, an FED (Field Emission Display) device, an LED(Light-Emitting Diode) display device, an electrophoretic migration, athin cathode-ray tube, a liquid crystal shutter, a device using adigital micro-mirror device (DMD), and the like. These electro-opticdevices can be applied to electronic devices, e.g., a personal computer,a cellular phone, a liquid crystal TV, a view-finder or direct-viewingmonitor type video tape recorder (camcorder), a car navigation device, apager, a PDA, a calculator, a word processor, a work station, a TVphone, a POS terminal, and an electronic device having a touch panel,among others.

[0201] Further, the electro-optic device and the electronic device arenot limited to the examples as shown above, and may be variouslymodified within the spirit of the present invention. The liquid crystalpanel according to the embodiments has a simple-matrix structure, andfurther is applicable to active-matrix electro-optic devices having anactive element, such as a TFT (thin-film transistor) or a TFD (thin-filmdiode).

[0202] Advantages

[0203] As mentioned above, the circuit board of the present inventioncomprises the pad, the wiring, and the soldering resist having theopening portion for exposing the pad and the wiring. Consequently, it ispossible to provide a circuit board in which the soldering material isprecisely coated to the pad on the circuit board with the wide marginand the mounting position of the BGA is not deviated.

[0204] Further, the mounting structure of the BGA according to thepresent invention uses the circuit board having the opening portion forexposing the pad and the wiring. Consequently, it is possible to providethe mounting structure to prevent the deviation of the mounting positionof the BGA.

[0205] Furthermore, the electro-optic device and the electronic deviceincluding it according to the present invention use the circuit boardhaving the opening portion for exposing the pad and the wiring.Therefore, it is possible to provide the electro-optic device and theelectronic device including it, in which the soldering defect issuppressed and the manufacturing efficiency is improved.

[0206] The entire disclosure of Japanese Patent Application No.2002-298980 filed Oct. 11, 2002 is incorporated by reference.

What is claimed is:
 1. A circuit board comprising: a pad for mounting aball grid array on said board; a wiring which connects said pad and anexternal terminal; and a soldering resist having an opening portionwhich exposes said pad and said wiring in a region on which said ballgrid array is mounted on said board.
 2. A circuit board of claim 1,wherein when an area of said ball grid array which is mounted on saidboard is 100%, an area of said opening portion is within a range of 50%to 150%.
 3. A circuit board of claim 1, wherein in the region in whichsaid ball grid array is mounted on said board, an end portion of saidsoldering resist is at least 0.1 mm inboard of an outer circumference ofthe region.
 4. A circuit board of claim 1, wherein when a pitch of abump of said ball grid array mounted on said board includes a narrowpitch portion less than 0.6 mm and a wide pitch portion not less than0.6 mm, said soldering resist has an opening portion corresponding tothe narrow pitch portion of said ball grid array.
 5. A circuit board ofclaim 1, wherein a thickness of said soldering resist is 1% to 50% of aheight of a bump of said ball grid array mounted on said board.
 6. Acircuit board of claim 1, wherein said board has a second pad formounting an electronic element other than said ball grid array on saidboard, said soldering resist adjacently exists around said second pad.7. A mounting structure for mounting a ball grid array comprising: acircuit board, said circuit board including: a pad for mounting a ballgrid array; a wiring connected to said pad; and a soldering resisthaving an opening portion exposing said pad and said wiring.
 8. Amounting structure of claim 7, wherein an under-fill is filled betweensaid ball grid array and said circuit board with the followingproperties: (1) volume resistance having a value within a range of 1×10⁶to 1×10²⁰ Ω·cm, (2) tensile strength having a value within a range of 1to 200 MPa, and, (3) Break stretch having a value within a range of 10%to 500%.
 9. An electro-optic device including a ball grid array, as oneof a driving element and a power supply element, mounted on a circuitboard, said electro-optic device comprising: a pad for mounting the ballgrid array; a wiring for connecting said pad and an external terminal;and a soldering resist having an opening portion exposing said pad andsaid wiring.
 10. An electronic device comprising: an electro-opticdevice according to claim 9; and control means which controls saidelectro-optic device.